Hot cathode for cathode ray tubes



Dec. 31, 1940.

K. SCHL ESINGER HOT CAIX-IODE FOR GATIEODE RAY TUBES Filed Feb. 26, 1957 Kurz Schlesi wegfim til Patented Dec. 31, 1940 UNITED STATES nor CATHODE FOR CATHODE RAY TUBES Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application February 26, 1937, Serial No. 127,893 In Germany March 12, 1936 3 Claims.

In cathode ray tubes, in which a reproduction of the cathode takes place on the luminous screen, as well as in other cathode ray tubes, in which a certain cross-section of the ray may not be exceeded, hot cathodes are required which have a geometrically defined emissive surface. Cathodes of this nature (see also application Ser. No. 619,283, filed June 25, 1932) are produced in practice by boring into a comparatively large metallic surface to be raised to a glowing temperature a recess of definite diameter for the reception of oxide, this spot of oxide then acting as optical cathode.

The applicants have found that the pressing of oxide into metal, for example nickel incandescent elements results in durable cathodes only up to a certain diameter of the spot. Beyond a diameter of the spot of oxide amounting to approximately mm. the oxide generally becomes loose. The oxide substance commences to warp, becomes brittle, and loses contactwith the metallic base. Cathodes of this nature give only a very small fraction of the calculated emission, and after a very short time become ineffective owing to the fact that their transverse inner resistances become too high.

The idea might be conceived of pressing the oxide substance firmly into the base by means of a wire. net placed over the same. These nets, however, would require to be very fine as compared with the said diameter of the spot of oxide, as regards both their size of mesh and the thickness of the wire. Fine nets of this kind are diflicult to obtain and to use. If the size of mesh and the size of the said opening are about the same, the position of the net in relation to the spot of oxide is never definite.

These difiiculties are overcome by the invention, which is illustrated, by way of example, in the accompanying drawing showing in Fig. 1 a top plan view; in Fig. 2 a sectional elevation along line 2-2 of Fig. 1 of a cathode designed according to the invention; and Fig. 3 is a bottom view of the construction.

According to the invention, there is stretched across a spot of oxide I, which is disposed in a hole bored into an incandescent nickel member 2, a wire cross, which is drawn over four file grooves 3 and consists of a wire of preferably the same material as 2, the diameter of which is small as compared with the diameter of the spot of oxide 1. The wire 4 forming the cross is preferably nickel wire of about 50,11. in diameter. The equality of the material prevents the wire from slackening upon variations in the tempersurface.

ature of the cathode. In elevational view (Fig. 2) the head of the cathode is first rounded off, and there are to be recognized the file cuts 3 within the upper rounded portion 2a and also the recess la for reception of the oxide. The nickel incandescent member 2 is furnished in the lower part with four lateral abutments 5, which are preferably pressed out from the same material. The wire 4 may then be looped crosswise below the abutments and over the cathode head I. 6 is the filament, which raises the incandescent head 2 to a glowing temperature. An insulating tube 1 separates the filament from the metal of the cathode.

The saturation emission of cathodes of this character increases in proportion to the emissive It is an essential feature that the wire is in metallic contact with the oxide surface, which is accomplished by the fact that the wire, after being stretched, is coated itself with oxide. Presumably the improvement in the transverse inner resistance in combination with the adhering power of the oxide attained mechanically is the reason for the constant effectiveness of cathodes of this nature.

I claim:

1. A thermionic cathode comprising a heater, element, a conductive sleeve member closed at one end surrounding said heater, an insulating member spacing the sleeve and the heater, said closed end of said sleeve having a substantially centrally located recess in the outer surface thereof, a material within the recess adapted to emit electrons when heated by said heater, a wire member of minute cross sectional area relative to the emitter extending transversely to the emissive area and in both mechanical and electrical contact therewith, and means for anchoring the ends of said wire upon, the sleeve member, whereby the emissive material is anchored in the recess and both electrical and thermal conductivity are established between the emissive material and the sleeve member.

2. A cathode element comprising a conducting body member having an internal recess extending into the body member for a substantial por tion of its length, a ceramic lining on the wall of said recess, a heater unit extending into the recess and insulated therefrom by the lining, said body member also having an outer recess located substantially opposite the internal recess, an electron emissive material supported in said outer recess and adapted to be heated by said heater unit to release electrons, and a plurality of spaced wire members of minute cross sectional maintained. and the emissive material is also retained securely in the outer recess.

3. The cathode construction claimed in claim 1 wherein the wire member is formed of a material having a coefiicient of thermal expansion substantially equal to that of the sleeve member.

KURT SCHLESINGER. 

